Displays have become ubiquitous. There is increasing interest in providing displays that provide high quality images. Characteristics of high quality images include accurate color rendering and high dynamic (luminance) range. Displays capable of displaying high dynamic range images are known as high dynamic range displays.
Many displays display color digital images specified by input signals. Color digital images are made of pixels, and pixels are made of combinations of components, typically combinations of primary color components (e.g. Red-Green-Blue) or of a luminance component and chrominance components (e.g. YUV). The components that make up an image define a color space. A channel in this context is an image made of just one component, which varies in intensity over the image. The part of a channel that contributes to a pixel of a color image may be known as a sub-pixel.
Because input signals have finite bandwidth, the components of digital images are represented as discrete levels within finite ranges. As a result, the number of possible combinations of components is also discrete. The discrete representation of components causes the set of possible colors corresponding to combinations of the components, known as the gamut, to be limited in both depth (how finely levels of color can be expressed) and range (how broad a range of colors can be expressed).
Displays display color images by emitting colored light. Displays typically generate a range of colored light by combining light of different component colors. Displays that generate a range of colors of light by combining component colored light can display colors in a gamut defined by the component colored light. The gamut will be defined by the maximum intensity of each component colored light, and the depth of intensity of each component colored light. In some displays component colored light is emitted from pixels of a spatial light modulator that is illuminated by a backlight. In some displays, component color light is controlled digitally, for example by digital driving values. The gamuts of these displays are finite and discrete.
It is often the case that the gamut of a display will differ from the gamut of input signals that provide images to the display. The display gamut may differ from the input gamut in both depth (how finely levels of color can be expressed) and range (how broad a range of colors can be expressed). In order for the display to display a high quality image, the specification of the image for the input gamut must be transformed to specify the image for the display gamut. This transformation may require adjusting the image specification to provide increased depth or decreased depth, and/or to provide increased range or decreased range. By way of example only, an image specified for an input gamut with a range that is lower than the range of the gamut of a display may be adjusted for the higher-range gamut of the display.
The process of transforming an image specification from an input gamut to a display gamut provides an opportunity to optimize the image for display on the display. In particular, transforming the image specification may comprise increasing the dynamic range and the color depth of the image. However, increasing the dynamic range and the color depth of the image can introduce negative image characteristics, such as color shifts, posterization and visible contrast artefacts.
There is a general desire to provide displays capable of displaying high-dynamic range images. There is a general desire to adapt image data signals for high dynamic range display. There is a general desire to provide systems and methods for ameliorating and/or overcoming negative image characteristics associated with adapting image data signals for high dynamic range display.